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“French fries and cola please!”- neuroscience of the food addiction

“All you need is love. But a little chocolate now and then doesn’t hurt.” – Charles M. Schulz

How elusive feelings of pleasure are created in the human brain? Which part of the brain is responsible for the activation and generation of these positive feelings? What are the neurotransmitters, and why they are playing an important role in our brain? Many things can cause satisfaction, even those necessary for survival, such as eating. Surprisingly, processed food affects human brains at a similar level as hard drugs do. Another bothering question is related to food types. Why do people become addicted to processed food (also called junk food) and not to the healthy one? Answers to all of this question are encrypted deep within the human brain. Here, based on neuroanatomy and neuroscience, we aim to shed light on the understanding of a pleasure process in the brain and its role in becoming addicted. We are concentrating on the food acting as a stimulus of pleasure.

Image credit: M. Osial

The pleasure source in the brain

The human brain is the most complicated machine known in the Universe. The understanding of brain functioning belongs to the greatest challenges of contemporary science [1].  It is constantly working and processing the information delivered from the world, even during sleep. It is responsible for life functions, thinking processes, and most of all, the reactions to different stimuli. Here, we concentrate exactly on the last one, and in particular, on the pleasure responses. Mostly, pleasure is linked to happiness. Since Ancient, Aristotle perceives the duality of happiness [2]. According to them, it consists of pleasure (hedonism) and well-lived life (eudaimonia). Feeling pleasure is not only related to psychology, but it is also strongly connected with biology (the reactions that take place in the human brain). And in this field, Charles Darwin is a pioneer scientific study of pleasure and affection. He analyzed the affective feelings [3]. In [4] it was shown that pleasure and displeasure are the prominent reactions in mammalian brains. In 1954 the so-called “pleasure centers” in the brain were discovered by James Olds and Peter Milner [5]. In Figure 1 the placement of the liking pleasure center in the human brain is presented. Many years later, it has been discovered that the main substance, which significantly improves neuronal information processing is dopamine, the so-called pleasure neurotransmitter [6].

Figure 1. The scheme of the pleasure center responsible for liking. The Cingulate Gyrus is involved in processing emotions and behavior regulation, Amygdala is responsible for emotions, Hippocampus participates in cognition. Lobe is divided into four sections, where each one plays a different role – frontal one is related to emotions, Fornix is a C-shaped bundle of nerves, and Cerebellum plays many roles, including emotions regulation and cognition. [Figure – M. Osial]

From the psychological point of view, pleasure is a complex psychic experience, which includes such ingredients as liking, wanting, and learning [7, 8]. It entails processes like memory, motivation, homeostasis, and pain. There are two categories of pleasure. The fundamentals connected with food and sexual aspects, and higher-order, which include monetary, artistic, musical, altruistic, or transcendent [9].

Pleasure neurotransmitter

One of the well-known neurotransmitters is dopamine, also called the neurotransmitter of pleasure, while the main function of this molecule stimulation of pleasure in the brain [10]. It has a variety of functions, but there is a specific one that makes dopamine so unique [11]. It plays an important role in the reward and motivation system. Each time we do something pleasant, eat tasty food, or think about something we like, the dopamine is released. Dopamine is released in the orbitofrontal cortex, and it generates a feeling of pleasure [12]. The process of dopamine release is shown in Figure 2. The hippocampus responds to dopamine by recording these memories of pleasure.

Did you know that diet may influence our mood and mental health? There is a connection between diet and depression. Lack of dopamine may lead to depression [13] and Parkinson’s disease [14]. On the other hand, its excess causes schizophrenia [15]. It is also worth mentioning that dopamine is highly addictive [16]. A proper diet has a positive influence on people affected by those diseases [17].

Figure 2. Dopamine is released in the brain, where it is transported from one neuron to another one through the synapse (space between neurons). [Figure – M. Osial]

On the other hand, it was shown that the brain reward system is active while people see the picture of their bellowed one [18]. You may ask a question of how this is related to food addiction, and the answer is simple. It is commonly known that love is one of the most powerful feelings that human beings can experience. Dopamine is one of the neurotransmitters, which allows us to fall in love. The same neurotransmitter is released while we eat certain types of food. One of them is chocolate. Surprisingly it has over 350 chemical compounds inside that influence the human brain. During its consumption, many substances are produced, that affect the brain. For example, tryptophan and serotonin create feelings of relaxation and temporarily improve the mood. Other ones, like flavonoids, cause effects similar to a mild painkiller like aspirin after two or three hours of consumption [19]. In turn, anandamide is a neurotransmitter that activates pleasure receptors in the brain. Short-term dark chocolate (with high flavanol content) consumptions may have benefits on our memory, and reaction time was better in comparison to eating a white one [20]. What is interesting, but not necessarily has a relationship, the countries with the highest chocolate consumption have more Nobel Prize recipients.

Food Addiction

Humans and all other heterotrophic organisms need to consume food to sustain their demand for energy and nutrients. Despite this, as it is commonly known, food is not always good for you. In recent decades obesity is on the rise throughout much of the developed world and it is becoming an ever more serious health crisis. This tendency cannot be attributed solely to genetic factors and for many, the widely used term “food addiction” has become an attractive explanation. This attitude places blame for the situation on the food industry for producing “addictive foods” and, similarly to how alcohol and nicotine addiction is dealt with, aims to fight obesity by regulating the industry and curtailing its influence on people’s eating habits. Recent new restrictions on junk food advertising in the UK can serve as an example [21]. But what exactly is “food addiction” and what biological mechanisms are the cause of this phenomenon?

“Food addiction” was first defined by Theron G. Randolph [22]. According to his definition, it is a specific adaptation that a person develops to one or more regularly consumed foods. It can produce symptoms descriptively similar to those of other addictive processes. Many of us may feel addicted to a certain type or types of foods, in particular highly processed foods, also called junk food. The most addictive food has to be tasty. Have you ever wondered why sometimes it is so difficult to refuse a slice of pizza, some ice cream, cake, sugared soda, cheeseburgers, French fries, popcorn, cheese, rolls, crunchy chips, fried chicken, chocolate, or cookies? One can assume that the addictive quality of junk food is related to the way it is processed, but some special chemical components, which are responsible for this characteristic have been identified [23]. A particularly strong example of addictive food is chocolate. It may evoke similar psychopharmacologic and behavioral reactions in susceptible persons as drug or alcohol abuse [24]. This phenomenon, known as chocolate cravings, can lead to excess consumption of the substance and resulting health issues. There is a strong body of accumulating evidence pointing to a net health benefit from routine consumption of dark chocolate [25], but the debate in the scientific community is still ongoing. The one certain thing is that due to the high calory density of chocolate it is excessive consumption may put a person at risk of obesity. When a person consumes junk food, the brain releases dopamine in the reward system. If the amount of dopamine is too high, the brain begins to remove receptors of that neurotransmitter to maintain proper balance. The more junk food we eat, the more dopamine is released, which in turn causes a decrease in the number of receptors. As an effect, the brain is more neurostimulator to reach the same level of reward as before and gets addicted. In fact, we can compare food addiction to drug or alcohol addictions, the biological mechanism is similar [26], while they influence the brain by co-opting existing primary reinforcement systems. Several factors can contribute to food addictions like a coping mechanism to relieve the painful emotions, disorders in family functioning, social pressure or isolation, and stressful life events.

Summary

Food is crucial for our survival. Even when we are full, we can still take pleasure in eating, since food and drinks activate the craving and pleasure in many ways. Pleasures are also linked to human happiness. During eating in our brain a reward in the form of releasing chemicals into the pleasure center arises. When we have eaten enough, our brain stops stimulating our pleasure centers. Addicted people have built some kind of tolerance, and a healthy amount of food prevents them from completing this process.

This article was the joint work of Ewa Klejman (Faculty of Chemistry, University of Warsaw), Krzysztof Kwiatkowski (Faculty of Chemistry, University of Warsaw), Agnieszka Pregowska (Institute of Fundamental Technological Research Polish Academy of Sciences), Lee Reid (British School Warsaw), Magdalena Osial (Faculty of Chemistry, University of Warsaw). Images – Magdalena Osial.

References

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